The present invention relates to a method and apparatus for controlling the flow of fluids through a heat exchanger in order to maintain the efficiency or effectiveness of the heat exchanger at a predetermined level that is selected with respect to the particular prevailing operational conditions. The inventive method and apparatus eliminate the requirement to use flow meters for measuring either of the two fluid flows through the heat exchanger, even if the flow of one of the fluids varies in an uncontrollable fashion with respect to time.
In many industrial processes there are produced large flows of fluid which have been elevated in temperature, such as heated waste water, and in which the flow of the fluid may exhibit large variations in the flow with respect to time. When the flow rate of the elevated temperature fluid is high, it is attractive to recover as much of the heat content of such fluid as possible by conducting it through a heat exchanger, preferably through a counter-current heat exchanger, and there to transfer the heat to another fluid, making it possible to utilize the heat absorbed in this second fluid. Should the flow rate of one of the fluids vary, then the flow rate of the other fluid also has to be adapted or adjusted correspondingly to keep the thermal transfer in the heat exchanger at or near an optimum value with respect to the particular prevailing operational conditions.
The solution to this problem which seems nearest at hand, and the one that is most commonly used, involves making direct fluid flow rate measurements and controlling the flow of one of the fluids in response to variations in the flow of the second fluid, as well as the other measured parameters. This direct measuring of fluid flow involves technical as well as economic problems in many applications, for example, when confronted with the large magnitudes of variations of fluid flow which may be present when recovering heat from the waste water in an industrial process.